The metallic strip bending devices known in the art, particularly those intended for the manufacture of die cutting blades, generally comprise a system for feeding the continuous metallic strip through a guide opening, near which one or more bending tools are arranged. Most commonly, two bending tools are provided, the one for providing the strip with the right (or for example upwards) bends and the other for providing the strip with the left (or for example downwards) bends.
The strip is advanced through the guide opening and temporarily stopped when a bend has to be performed. The bending tool, which is arranged near the guide opening, is then rotated to provide the strip with the right (or left) deformation for a predetermined angle, as desired.
A double-tool bending system is described, for example, in the U.S. Pat. No. 5,870,919, in which the bending tools are engaged in suitable seats of co-axial holders that are arranged opposite the guide opening, and caused to rotate about their common axis. The bending tools can be retractable, and thus can be used in a mutually exclusive manner, i.e. a tool is held in the working position while the other is held in the rest position. Another example of a double-tool bending system is described in the U.S. Pat. No. 6,629,442 in which each tool is held by a pair of co-axial holders rotating about their common axis. The holders of a pair are arranged alternating with those of the other pair, and consequently, at least two of them are required to have an engaging seat for the bending tool being held, as well as a groove for allowing the other to move.
One of the problems involved with the known bending systems is that, during the bending step, the tool that is carrying out the bending moves away from the bending point while rotating, thereby a relative sliding movement is caused between the tool contacting the strip and the strip itself. This entails considerable wear of the bending tools, and thus the tools need to be replaced quite frequently in order to ensure the required process accuracy.
As the bending tools are very complex systems from a mechanical point of view, they may require a very long time for replacement, which may affect productivity.
In addition, it should also be noted that a tool is subjected to a stress that increases proportionally to the bending angle to be obtained. The wear effects on the tool are thus considerable, when manufacturing products with particularly sharp bending angles.
The task of the present invention is to provide a device and method for bending metallic strips, which allow to overcome the drawbacks of the prior art.
Within this task, an object of the present invention is to provide a method and device of the above-mentioned type, which allow to avoid the relative sliding motion between the bending tools and the metallic strip during the bending steps.
Another object of the present invention is to provide a method and device of the above-mentioned type which allow to hold the tool always in the most effective position, regardless of the bending angle to be obtained.
A further object of the present invention is to provide a method and device of the type mentioned above, which however allow to provide very close bends, also in the opposite directions, and also for high bending angles.